Despite the facts that newborns, infants and older children have greater ventilation per unit of body weight and that modeling efforts indicate that they generally receive greater doses from inhaled particles than do adults, there are no validated aerosol inhalation dose models for pre-adults. The proposed research is intended to remedy this deficiency. Research will be conducted in two areas; performing aerosol deposition experiments in adult- and child-sized hollow airway models, and application of computational models to children. These two efforts are mutually supportive because the hollow model data can be used to validate and/or modify the computational models, and the computational models can be used to identify the hollow model features that strongly determine particle deposition. The scope includes the particle aerodynamic diameters of most interest in toxicology (0.1 to 20 micrometers), ages 0 years to adult, several states of activity (resting to heavy exertion), and as the study proceeds, atypical anatomical or physiological features, non-ideal particles, and mixtures of pollutants. Laboratory studies will use hollow models which are designed from anatomical data on growing people, and which take into account the critical structural features that are known to influence the major aerosol deposition mechanisms (impaction, diffusion and sedimentation). The models will be subjected to laboratory-generated aerosols of known sizes at controlled airflows and particle deposition will be measured. The computational models will be based on models known to be valid for adults and they will include sequential deposition in each of the anatomical regions. The inspirability of airborne particles of various sizes will be included in the computational model. Existing computational models will be improved as part of the project. The results will include aerosol deposition efficiencies in hollow models of various sizes that represent regions of the respiratory tract (nasal, oral, pharyngeal, laryngeal, and tracheobronchial). Results will also include dosimetric computations for these regions (and the alveolar region) for various ages and states of activity.